As a winch device mounted on a crane to perform hoisting work (crane work), there has been known an electric winch device driven by an electric motor to hoist a target object of the hoisting work. As the electric winch device, there has been known an electric winch device including a regeneration function for converting kinetic energy generated by a fall of a target object during the lowering of the target object into electric energy and collecting the electric energy.
Patent Literature 1 described below discloses an example of the electric winch device including such a regeneration function. The electric winch device disclosed in Patent Literature 1 includes a winding drum that winds a wire for suspending a hook block and an electric motor that rotates the winding drum in a hoisting direction of the hook block. During the lowering of the hook block, the electric motor generates regenerative electric power and the generated regenerative electric power is consumed by a power consuming system connected to the electric motor.
Incidentally, in a mobile crane, an electric winch device capable of implementing a freefall of a target object to be dropped in a nearly free fall state of the target object is sometimes used. When such an electric winch device includes the regeneration function, regenerative electric power is generated by the electric motor during the freefall of the target object.
Falling speed of the target object during the freefall is large compared with speed of the target object during the hoisting of the target object. Therefore, the regenerative electric power regenerated by the electric motor during the freefall of the target object is larger than power-running electric power supplied to the electric motor during the hoisting of the target object. As a height position of the target object is higher, a difference between regenerative electric power regenerated by the electric motor during a freefall of the target object from the height position and power-running electric power required by the electric motor to hoist the target object to the height position is larger.
Since the regenerative electric power during the freefall of the target object is larger than the power-running electric power during the hoisting of the target object as explained above, allowable electric power such as rated electric power or maximum electric power of the electric motor has to be set on the basis of a maximum of the regenerative electric power during the freefall. Moreover, when the difference between the regenerative electric power during the freefall of the target object and the power-running electric power during the hoisting of the target object expands as explained above, that is, when the maximum of the regenerative electric power during the freefall of the target object increases, an extremely large value is requested as the allowable electric power of the electric motor to make it possible to cope with the increase in the maximum of the regenerative electric power.
Therefore, the electric motor used in the conventional electric winch device not including the freefall function cannot cope with the increase in the maximum of the regenerative electric power. An electric motor having large allowable electric power capable of coping with the regenerative electric power during the freefall is necessary. Such an electric motor having large allowable electric power is large and expensive. In order to control the electric motor having the large allowable electric power, large and expensive components for control such as an inverter are also necessary. Therefore, the electric winch device increases in size and the manufacturing cost of the electric winch device increases.